The present invention relates to an instrument for measuring the concentration of a specific component of blood, in particular, to a blood sugar determining instrument for measuring the concentration of glucose in blood.
In recent years, various kinds of biosensors utilizing a specific catalytic action of enzymes have been developed to be used for clinical purposes. Most valuable use of such biosensors may be made in the area of e.g. diabetes treatment where it is vital for patients to keep their blood glucose concentration (xe2x80x9cblood sugar levelxe2x80x9d below) within a normal range. For an inpatient, the blood sugar level can be kept normal under the supervision of the doctor. For an outpatient, self-control of the blood sugar level is an important factor for treatment in lack of doctor""s direct supervision.
The self-control of the blood sugar level is achieved through a diet, exerciseand medication. These treatments may often be simultaneously employed under the supervision of the doctor. It has been found that the self-control works more effectively when the patient himself is able to check whether or not his blood sugar level is within the normal range.
Recently, blood sugar determining instruments have been used for self-checking of blood sugar level. As shown in FIG. 1, a blood sugar determining instrument mainly includes a main detecting unit 1 and a chip 2 for blood sugar measurement. As shown in FIGS. 2 and 3, the chip 2 includes a strip-like substrate 15 provided in its front portion with an electrode section 4. The electrode section 4 is covered by a reaction layer 5, a spacer 6 and a cover sheet 7. The electrode section 4 is provided with an operational terminal 11 and a counterpart terminal 12 surrounding the operational terminal 11. The operational terminal 11 and the counterpart terminal 12 are electrically connected to lead terminals 13 and 14, respectively, which are formed on a base end portion of the substrate 15. The reaction layer 5, which covers the electrode section 4, contains potassium ferricyanide and an oxidase such as glucose oxidase.
The blood measuring instrument may be used in the following manner. A patient pricks his or her own skin with e.g. a lancet for oozing blood. Then, the oozed-out blood is caused to touch the tip of the chip 2 plugged into the detecting unit 1. The blood is partially sucked into the reaction layer 5 by capillary action. The reaction layer 5, disposed above the electrode section 4, is dissolved by the blood, which starts an elementary reaction.
The potassium ferricyanide contained in the reaction layer 5 is reduced, whereas potassium ferrocyanide or reduced electron carrier is accumulated. The amount of the potassium ferrocyanide is proportional to the concentration of glucose to be measured. When the potassium ferrocyanide accumulated for a specific time is electrochemically oxidized by application of a certain voltage, a response current will pass through the operational terminal 11. Thus, the glucose concentration (blood sugar level) is determined by measuring the response current with the detecting unit 1. As shown in FIG. 6a, the chip 2 is plugged into a connector 3. The connector 3 is internally provided with connection terminals 21 to come into contact with the lead terminals 13, 14 for detection of the response current flowing through the operational terminal 11. The detected current is converted into a glucose concentration value by a computer incorporated in the detecting unit 1.
The terminals 11, 12, 13, 14 on the chip 2 are formed only on one side of the chip 2, so that these terminals 11, 12, 13, 14 are readily formed by screen printing. Thus, the manufacturing process is preferably simplified, which serves to lower the costs of consumable chips.
However, the one-side formation of the terminals 11, 12, 13, 14 can be disadvantageous in inserting the chip 2 into the connector 3 of the detecting unit 1 upside down. As shown in FIG. 6b, the lead terminals 13, 14 on the chip 2 may fail to be connected to the connection terminals 21 in the connector 3. In such an instance, proper measurement cannot be performed by the blood sugar determining instrument.
Diabetics may often be elderly people and/or have weak eyes, so that many of them may have difficulty in distinguishing one surface of the chip 2 from the other. In light of this, the chip 2 may be provided with side-discerning means. For instance, the chip 2 may be provided with a cut out or protrusion formed on one side. Alternatively, the measuring instrument may be so arranged that the chip 2, when held upside down, cannot be inserted into the detecting unit. In any case, the chip needs to be inserted properly, i.e., without having its obverse and reverse surfaces turned over. Disadvantageously, the formation of a cutout or protrusion will require additional steps for making the chips, which results in a cost increase.
It is an object of the present invention to provide a blood measuring instrument, wherein a chip can be inserted into a detecting unit without undergoing the surface-discerning step.
A blood measuring instrument according to the present invention comprises: a plate-like chip for drawing sampled blood; and a main detecting unit having a connector into which the chip is inserted. The chip includes, on a single side, an enzyme electrode section for passing a response current in response to a specific component of the blood, and lead terminals electrically connected to the enzyme electrode section. The main detecting unit includes two sets of connection terminals which are disposed within the connector and engageable with the lead terminals of the chip, wherein the two sets of connection terminals are held infacing relation to each other.
According to the present invention, the connector of the main detecting unit is internally provided with two sets of connection terminals engageable with the lead terminals on the chip, and these two sets of connection terminals are held in facing relation to each other. When the chip is plugged into the connector, either one of the two sets of connection terminals is connected to the lead terminals formed on a selected side of the chip. Thus, proper blood measurement is carried out whether the chip inserted into the main detecting unit faces upward or downward.
In a preferred embodiment, the enzyme electrode section includes a reaction layer dissolved by the blood and an electrode pattern which has an operational terminal for passing the response current and a counterpart terminal surrounding the operational terminal. The reaction layer covers the operational terminal of the electrode pattern.
When the blood is applied onto the chip, the reaction layer is dissolved by the blood, which starts an enzyme reaction. Thus, electron carriers are generated correspondingly to the concentration of the specific component (e.g. glucose) of the blood. After a certain period of time, a voltage is applied to the chip, whereby a response current is generated in the operational terminal of the electrode section. For measurement, the response current is supplied to the main detecting unit through the lead terminals and the connection terminals of the connector. The response current is proportional to the concentration of the specific component of the blood. Thus, the concentration of the specific component is calculated on the basis of the response current value by using a calibration curve prepared beforehand.
In a preferred embodiment, the reaction layer contains glucose oxidase or lactate oxidase as an oxidase and potassium ferricyanide as an electron acceptor.
For determining the glucose concentration in blood (blood sugar), the oxidase in the reaction layer is glucose oxidase and the electron carrier is potassium ferricyanide. In enzyme reaction, the glucose is turned to be gluconic acid, while the potassium ferricyanide is reduced to potassium ferrocyanide. The amount of potassium ferrocyanide is proportional to the concentration of the glucose to be measured. After a predetermined period of time, the potassium ferrocyanide is electrochemically oxidized by applying a voltage to the chip. Then, the resulting response current is converted to the glucose concentration.
For determining the lactic acid concentration, the oxidase in the reaction layer is lactate oxidase, while the electron carrier is potassium ferricyanide. In enzyme reaction, the lactic acid is turned to be pyruvic acid, while the potassium ferricyanide is reduced to potassium ferrocyanide. The amount of the potassium ferrocyanide is proportional to the concentration of the lactic acid to be measured. After a certain time, the potassium ferrocyanide is electrochemically oxidized by applying a voltage to the chip. Then, the amount of the resulting response current is converted to the lactic acid concentration.
As described above, according to the blood measuring instrument of the present invention, it is unnecessary to worry about whether or not the chip is held upside down in inserting the chip into the connector of the main detecting unit. It is much easier for weak-sighted or elderly patients to use the blood measuring instrument of the present invention than the conventional instrument, since there is no need to check the orientation of the obverse or reverse surface of the chip.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.